CHARCURVE

This function block ( The library UTIL.Library\ \) serves to represent values, piece by piece, on a linear function:

Example in FBD\ \ \ \

IN of type INT is fed with the value to be manipulated.

N of type BYTE designates the number of points which defines the presentation function.

P of type ARRAY P[0..10] OF POINT, which is a structure based on two INT values (X and Y), determines this characteristic curve.

OUT of type INT contains the manipulated value.

ERR of type BYTE indicates an error.

The points P[0]..P[N-1] in the ARRAY must be sorted according to their X values, otherwise ERR receives the value 1. If the input IN is not between P[0].X and P[N-1].X, ERR=2 and OUT contains the corresponding limiting value P[0]. Y or P[N-1].Y.

If N lies outside of the allowed values which are between 2 and 11, then ERR=4.

Example in ST:\ \ \ \

First of all ARRAY P must be defined in the header:

VAR

...

CHARACTERISTIC_LINE:CHARCURVE;

KL:ARRAY[0..10] OF POINT:=[(X:=0,Y:=0),(X:=250,Y:=50),

(X:=500,Y:=150),(X:=750,Y:=400),7((X:=1000,Y:=1000))];

COUNTER:INT;

...

END_VAR

Then we supply CHARCURVE with for example a constantly increasing value:

COUNTER:=COUNTER+10;

CHARACTERISTIC_LINE(IN:=COUNTER,N:=5,P:=KL);

Illustration of the resulting curves: